Experimental and semiemprical studies of chemical reactivity of dialkylcadmium reagents addition to α,β-enones

Experimental and semiempirical calculations were carried out to study the reactivity of dialkylcadmium reagents addition to α,β-enones. It was demonstrated that α,β-enone such as benzoquinone with low lying LUMO energy reacts via single electron transfer (SET) mechanism with the formation of the 1,2 or 1,4-type alkyl addition product depending on the reaction temperature and substrate structure. Site and chemoselectivity in unsymmetrical benzoquinone derivatives are determined by the stability of the cadmium coordinated semienone complex intermediates and the carbon spin densities of these reactive species respectively. On the other hand, by increasing the LUMO energy of α,β-enone system, the reaction mechanism changes from SET to polar addition affording the 1,4-type alkyl addition product. The establishment of a correlation scale between substrate LUMO energies and reaction mechanism presented in this article will be discussed.